The present invention relates generally to contact assemblies, and more particularly, to a one-piece meter jaw and to meter socket assemblies incorporating such jaws, such as for use in a socket for a direct-reading watt-hour meter. This type of socket is known in the trade as an “S” type meter socket. It has a standardized form to allow the interchangeability of meters from various manufacturers without removing any wires or cables. A watt-hour meter having a typical pattern of a pair of parallel sets of aligned connector blades is shown in U.S. Pat. No. 4,104,588, which is incorporated herein by reference. While such a meter socket is employed for meters capable of continuous full load currents of 20 to 400 amperes, it is most typically utilized for residential applications at 200 amperes.
In standard plug-in “S” type meter sockets, a watt-hour meter is plugged into a meter socket which is mounted in an enclosure. This configuration must provide means to make the electrical connection to the incoming and outgoing power cables or bus bars. In this type of meter socket, the electrical connections to the meter, as well as the retention of the meter in the meter socket, is performed solely by a plurality of meter jaws. These jaws are electrically connected to means for electrical connection to the power cables or bus bars. Because these jaws and connectors are all connected to separate electrical potentials, they must be fixedly supported by one or more insulating mounting bases or blocks, which are in turn secured to the enclosure.
In one known configuration, the meter jaws are constructed of flat metal that is formed to create a conductive receiving jaw in such a manner that there is a resulting compressive force which is required to retain the meter blades in the jaws. The compressive force must be sufficient to reduce the heating that will occur as current is passed through the watt-hour meter, but must be low enough to permit installation of the meter into the meter socket and removal of the meter therefrom. Some specifications require that the force required to insert the meter, which may have from 4 to 7 meter connections, into the meter socket be less than 100 pounds. The selection of materials for such jaws is a compromise. The metal must have high electrical conductivity to reduce the resistive heating effects and high thermal conductivity to permit conduction of the heat out of the meter sockets through the power cables. It must also be relatively short and thick to lower its bulk resistance to minimize the heating effects. On the other hand, the mechanical form of the meter jaw must be such that the yield strength of the material is not exceeded as the meter blade is engaged to such an extent that the jaw does not substantially return to its initial geometry when the meter blade is retracted or an additional supplemental spring component would be required. In order to insure these mechanical characteristics, the mechanical form of the jaw should be relatively long and thin in cross-section. The conductive element is often chosen to be a bronze, brass, beryllium-copper, or other alloy rather than copper or aluminum, which are more electrically and thermally conductive.
Because of these trade-off characteristics, many meter jaw designs employ additional separate components which function as springs to supplement the compressive forces provided by the electrically conductive elements of the meter jaws. Additional components are also used to guide the meter into the jaws and to electrically and/or mechanically connect the meter jaw, electrical connector, mounting base and enclosure.
FIG. 1 shows a typical modern meter socket jaw assembly 200 for use with power cables. There are typically four of these assemblies in a meter socket, although there may be as many as six current-carrying jaws in an “S” type socket. A wire connector 202 is electrically and thermally coupled to meter jaw 204 by a stud 206 and meter guide/jaw nut 208. A slide nut 210 engages a pair of receiving grooves 214 in the connector 202, and slide screw 216 acts to force stranded wire placed in connector 202 into good mechanical, electrical and thermal contact with connector 202. A back-up spring 218 is optionally used to improve contact force and lower joint resistance with the meter socket. It is located inside the meter jaw 204 by a hole that cooperates with the stud 206. Note that there are 7 or 8 components per conductor, or at least 28 such components in a 4 terminal meter socket. A securing nut 220 is used to retain the assembly 200 to a mounting block 226 in FIG. 2.
FIG. 2 shows additional components that are required. These are used to insulate the electrical components from an enclosure 228 (FIG. 3) which will house the meter jaw assemblies 200, to secure the components to the enclosure 228, and to provide the required grounding connection (not shown) to the watt-hour meter. The insulative mounting blocks 226 receive the assemblies 200 described in FIG. 1. Wire meter supports 230 are located by mating bosses and grooves in the mounting block 226. The mounting blocks 226 are then secured to a mounting bridge 232 by the four mountings screws 234. The mounting bridge 232 with all components installed is secured to the enclosure 228 by mounting screws 236. In typical meter sockets, these represent an additional 11 components. In some applications three of these components are not required (mounting bridge 232 and 2 mounting screws 236).
FIG. 3 shows the remaining components of a typical modern meter socket. They include the enclosure 228 and a cover 240. The cover 240 has latch 242 rotationally fixed by rivet 244 to cooperate with a tab in enclosure 228 to seal the enclosure. The cover 240 has a flange 246 surrounding an opening through which a cylindrical, glass covered portion of the watt-hour meter extends. The cover flange 246 engages a corresponding flange on the meter when the cover 240 is latched to thereby retain the meter against the wire support 230.
The prior art meter socket described above has several disadvantages. Firstly, the use of a high number of components acts to reduce reliability. Secondly, the high number of components acts to increase assembly costs. Yet another disadvantage of the current art is the temperature rise permitted. Agencies such as Underwriters Laboratories specify temperature rise limits for meter sockets and their components. A limit is specified for the connector to insure that connecting cable insulation or bus bars are not damaged or degraded. A 10 degree Centigrade higher limit is imposed on the meter jaw to insure that watt-hour meters are not degraded or damaged. Most current art meters exhibit this 10 degree difference. It is the result of the geometry of the meter jaw and its electrical and thermal conductivity. Many modern watt-hour meters employ semiconductor electronic components. These and other electronic components exhibit reduced life phenomena at increased temperatures.